1. Field of the Invention
The present invention relates to a liquid crystal display device and more particularly to a liquid crystal display device with a restricted viewing angle.
2. Discussion of the Related Art
A liquid crystal display (LCD) includes a first substrate, a second substrate, and a liquid crystal layer. The first and second substrates are facing each other and spaced apart from each other with the liquid crystal layer interposed between the first and second substrates. The LCD device uses optical anisotropy and polarization properties of the liquid crystal molecules to display images.
The liquid crystal molecules have a thin and long orientation. Moreover, a direction of the liquid crystal molecule arrangement may be controlled by applying an electrical field to the liquid crystal molecules. Herein, the LCD device may include a thin film transistor (TFT) as a switching element. This device is referred to as an active matrix LCD (AM-LCD) device which has excellent resolution and superior moving image display characteristics.
FIG. 1 is an exploded perspective viewing of an LCD device according to the related art.
As shown in FIG. 1, the first and second substrates 110 and 120 face each other, and the liquid crystal layer 130 is interposed between the first and second substrates 110 and 120. The first substrate 110 includes gate lines GL, data lines DL, thin film transistors (TFT) a “T”, and pixel electrodes 112. The gate lines GL and the data lines DL cross each other such that sub-pixel regions PA are defined by the gate and data lines GL and DL. The TFTs “T” are formed at respective crossing portions of the gate and data lines GL and DL, and the pixel electrodes 112 are formed in the respective sub-pixel regions PA and connected to the corresponding TFTs “T”.
The second substrate 120 includes a black matrix BM, color filter layers 126, and a common electrode 122. The black matrix BM has a lattice shape to cover a non-display region of the first substrate 110 that includes the gate line GL, data lines DL, and the TFTs “T”. The color filter layers 126 includes first, second, and third sub-color filters 126a, 126b, and 126c, respectively. Each of the sub-color filters 126a, 126b, and 126c has one of red, green, and blue colors “R”, “G”, and “B”, and each corresponds to a respective sub-pixel region PA. The common electrode 122 is formed on the black matrix BM and the color filter layers 126 as well as being formed over an entire surface of the second substrate 120. The arrangement of the liquid crystal molecules is controlled by a vertical electric field between the pixel electrode 112 and the common electrode 122, thereby resulting in a change of the amount of transmitted light. Thus, the LCD device displays images. Accordingly, the LCD device using the vertical electric field has a high transmittance and a high aperture ratio. However, the LCD device may include problems such as narrow viewing angle and low contrast ratio.
To resolve the above-mentioned problems, new display devices may include an in-plane switching (IPS) mode LCD device using a horizontal electric field or a vertical alignment (VA) mode LCD device vertically aligning the liquid crystal molecules to the substrate.
FIGS. 2A and 2B show the IPS mode LCD device and the VA mode LCD device, respectively, according to the related art.
In FIG. 2A, the IPS mode LCD device may include first and second substrates 210 and 220 facing each other, and the liquid crystal layer 230 interposed between the substrates. Both the pixel electrode 212 and the common electrode 222 are formed on the first substrate 210 such that the electric field is horizontally formed between the pixel electrode 212 and common electrode 222. The liquid crystal molecules are controlled by the horizontal electric field between the pixel electrode 212 and common electrode 222. Because a reflective index is relatively uniform at any viewing point, the viewing angle improves.
In FIG. 2B, the VA mode LCD device may include first and second substrates 260 and 270 facing each other with the liquid crystal layer 280 interposed between the first and second substrates 260 and 270. The pixel electrode 262 is formed on the first substrate 260, and the common electrode 272 is formed on the second substrate 270. In an initial state, the liquid crystal molecules in the liquid crystal layer 280 are vertically arranged with respect to the first and second substrates 260 and 270. In addition, a slit 274 is formed in the common electrode 272. An electric field 290 is symmetrically formed between the pixel electrode 262 and common electrode 272 wherein multi-domains are formed. Accordingly, the viewing angle is increased. Because the IPS mode and VA mode provide an improved viewing angle, viewers may see a similar image at a variety of viewing angles.
However, for an automatic teller machine, the LCD display of the automatic teller machine should not be viewable by a person other than the teller machine user. Accordingly, the viewing angle should be restricted so that only the automatic teller machine user can see the image displayed. One method of restricting the viewing angle uses a filter. Unfortunately, this method increases power consumption, production time, and production costs of the LCD device.